Interpretive Summary: Peach canker is a major disease of peach in the southeastern US and can substantial yield loss and rejection of fruit for fresh sale. The aim of this study was to describe and quantify the distribution of lesions on the fruit surface, and provide evidence of the epidemiological processes involved in the development of disease on peach fruit. Fruit of four cultivars, Jerseyqueen, Jefferson, 07-6428R and Dixieland, were collected and the fruit sliced taking four horizontal planes across the axis from the point of maximum disease. Lesions were counted on each zone of the fruit. The varieties differed in fruit size and lesion counts. Fruit of each cultivar had lesions on every zone, but the mean percent of lesions on the four varieties on each of the zones demonstrated that most lesions were found on upper most zone. Measurements of the point of maximum disease relative to the peduncle-flower scar axis of the fruit suggest that fruit are not always held upright when infection occurs. The pattern of disease is consistent with observations of the splash-borne nature of conidia, and the need for surface moisture on peach fruit (the most exposed uppermost portion of fruit generally being the most easily wetted). Management strategies to minimize splash, inoculum dispersal and reduce infection, including the use of fungicides will help reduced disease on fruit, particularly on the upper surfaces that are most prone to infection.

Technical Abstract:
Peach canker (Fusicladium effusum) can cause yield loss of peach and results in rejection of fruit for fresh sale. Developing peach fruit become infected through splash dispersed inoculum. The aim of this study was to describe and quantify the distribution of lesions on the fruit surface, and provide evidence for the processes involved in the development of disease on peach fruit. Fruit of four cultivars, Jerseyqueen, Jefferson, 07-6428R and Dixieland were collected and the fruit (assumed spherical) sliced taking four horizontal planes across the axis from the point of maximum disease, such that each horizontal zone (Z1-Z4) had the same vertical height, and thus equal surface areas. Lesions were counted on each zone of the fruit, and the varieties differed in fruit size and lesion counts (P<0.0001). Some fruit of each cultivar had lesions on every zone, but the mean percent of lesions on the four varieties on Z1 (65-81%) Z2 (16-27%) Z3 (3-7%) and Z4 (0-2%) demonstrated that most lesions were found on Z1. Measurements of the point of maximum disease relative to the peduncle-flower scar axis of the fruit suggest that fruit are not always held upright when infection occurs, such that up to 40% of fruit showed maximum infection at an angle >90° to the peduncle. This pattern of disease is consistent with observations of the splash-borne nature of conidia, and the need for surface moisture on peach fruit (the most exposed uppermost portion of fruit generally being the most easily wetted). Management strategies to minimize splash, inoculum dispersal and reduce infection, including the use of fungicides will help reduced disease on fruit, particularly on the upper surfaces that are particularly prone to infection.